The present invention is directed to an improved lifetime membrane system for separating a gasoline feed stream using a pervaporation membrane. Such a system has potential for application to an “on-board” separation system for multiple fuel feed as illustrated in U.S. Pat. No. 7,803,275, for example.
Pervaporation is a well-known membrane process. Pervaporation has been and is being considered for low energy consumption separation of aromatics from streams. A multicomponent liquid feed may be separated based on a selective solution-diffusion mechanism, with the permeate removed as a vapor, retentate typically remaining a liquid.
Gasoline is a complex mixture of aliphatic and aromatic hydrocarbons, often with oxygenates such as ethanol, having a wide boiling range. Aromatics and oxygenates such as ethanol may be separated from a gasoline feed by pervaporation to obtain a higher-octane fuel. However, the wide boiling range, variable composition and volatility of market gasolines make separation with simple pervaporation membrane systems difficult and inefficient. Maintaining sufficient membrane flux and selectivity is a challenge. Conventional gasoline typically contains additives, and other high boiling constituents, that may benefit its use in conventional internal combustion engines, but have deleterious effects on sustained membrane performance.
Other separation systems have used complex systems including pre-fractionation, multi-stage membrane processing, and/or recycle with post-fractionation, to address these issues, but are generally not desirable for efficient or commercially cost effective membrane systems.
The present invention enables considerable simplifications to the pervaporation process, when separating wide boiling range feeds such as gasoline having conventional additives, for example. These simplifications can lead to the reduced cost and system complexity, while increasing the longevity of the pervaporation membrane to enable commercialization of this application.